Interstitial lung disease associated with combination therapy of dabrafenib and trametinib in metastatic BRAFV600E-mutated poorly differentiated thyroid cancer: A case report and review of the literature.

Background: Thyroid cancer is the most common malignancy of the endocrine system, accounting for ~ 5% of all thyroid nodules and 1% of all systemic malignancies. BRAF mutations, primarily p.V600E hot spot mutations, are found in 60 - 70% of papillary thyroid cancer cases (PTC) and in 33 - 40% of fatal anaplastic thyroid cancers (ATC), also called poorly differentiated thyroid cancer. Dabrafenib was approved by the United States Food and Drug Administration (FDA) in 2018 to be applied in combination with trametinib for unresectable advanced or metastatic anaplastic thyroid cancer harboring the BRAF^V600E mutation. Unfortunately, there are few reports on the pathophysiology, molecular mechanism, and risk factors of interstitial lung disease induced by combined BRAF- and MEK-targeted therapy.

Case presentation: We treated a 73-year-old man with metastatic BRAF^V600E-mutated poorly differentiated thyroid cancer using the combination of dabrafenib and trametinib. Although a significant morphologic tumor response was observed in our patient using combined BRAF- and MEK-targeted therapy, he presented with non-febrile respiratory failure, and his chest computed tomography (CT) revealed bilateral reticulation and pleural effusion. Withdrawal from dabrafenib-trametinib and administration of methylprednisolone rapidly improved his respiratory status and imaging features.

Conclusion: The mechanisms of lung disease after the combined treatment with dabrafenib and trametinib are unclear. We hypothesized that dual-targeted therapy with a BRAF inhibitor, dabrafenib, and a MEK inhibitor, trametinib, might prevent the regeneration and proliferation of fibrotic epithelium in lung disease by blocking downstream proliferative signals.